It is known in the art to fabricate two piece plastic foam cups from frusto-conical blanks of sheet foam material seaming the blank to form a sidewall seam and placing a bottom blank at one end thereof and forming an additional bottom seam to complete the cup structure. It is also known in the art to place this entire cup structure in a steam-heated conformal mold to expand the foam sheet material either for the purpose of forming surface zones of higher density than the internal zones in the foam sheet material of the sidewall or for the purpose of actually heat sealing the various side and bottom seams.
All of these prior art structures require a single layer of foam of a sufficient caliper to insure sufficient stiffness and foam density in a given cup structure.
It is an object to the present invention to provide a two-piece plastic foam cup structure of the heat treated variety which is formed from a rectangular blank and which may be fabricated from a thinner caliper foam than has heretofore been possible to produce cups of the proper stiffness and foam density.
It is a further object to the present invention to produce a new and novel pleated sidewall cup structure.